Mix the onion powder, garlic powder, paprika, salt, and black pepper in a small bowl to create a seasoning blend. Rub this mixture evenly over both sides of the chicken thighs.
Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the chicken thighs, skin side down, and cook for 5-6 minutes per side until golden brown. Remove the chicken and set aside. Scrape out any burned bits from the bottom of the pot.
In the same skillet, add the diced onion and minced garlic. Sauté for 1-2 minutes, stirring frequently, until they soften. Stir in the tomato paste and cook for 1 minute to deepen the flavor.
Add the rice to the skillet with the onion mixture and stir to coat in the flavors. Toast the rice for 2-3 minutes, stirring occasionally.
Pour in 4 cups of chicken stock or vegetable broth and stir well to combine.
Place the chicken thighs back into the skillet, arranging them on top of the rice. Cover the skillet with a tight-fitting lid, reduce heat to medium-low, and let it simmer for 20-25 minutes, or until the rice has absorbed the liquid and the chicken reaches an internal temperature of 165 degrees F.
If the chicken isn't fully cooked after simmering, preheat the oven to 350 degrees F and transfer the covered skillet inside. Bake until the chicken is fully cooked through.
Turn off the heat and let the dish rest, covered, for 5 minutes. This allows the rice to absorb any remaining liquid and enhances the texture.
Fluff the rice gently with a fork, and serve the chicken and rice hot.